Earlier patent applications originating with our research group have disclosed catalysts endowed with high activity and high stereospecificity, obtained from metalorganic Al compounds, silicon compounds containing Si-OC, Si-OCOR or Si-NR.sub.2 bonds and a solid comprising a halogenated Ti compound and an electron-donor compound, both supported on an active Mg halide, the electron-donor compound being selected from specific classes of esters.
I have now found, unexpectedly, that it is possible to obtain highly active and stereospecific catalysts by employing, in the preparation of the catalysts disclosed in the previous patent applications, supported solid components comprising new classes of activators as indicated hereinafter.
The catalysts of the invention comprise the product of the reaction between at least the following components:
(a) an Al-alkyl compound, preferably an Al-trialkyl or a compound containing two or more Al atoms linked to each other through oxygen or nitrogen atoms or through SO.sub.4 or SO.sub.3 groups; PA1 (b) an electron-donor compound (or Lewis base) which, under the standard conditions of measurement as specified hereinafter, reacts with MgCl.sub.2 but results not to be completely complexed with Al-triethyl at the equivalent point of a potentiometric titration; PA1 (c) a solid comprising a Ti compound containing at least a Ti-halogen bond, supported on an anhydrous Mg halide and at least one of the following activators in an amount not lower than 5% by mols with respect to the Mg halide; PA1 R is an alkyl, alkenyl, aryl, arylalkyl or cycloalkyl with 1-20 carbon atoms; PA1 Y is a radical --OR', --OCOR' or --NR'.sub.2 wherein R', equal to or different from R, has the same meaning as R; PA1 X is a halogen or hydrogen atom or a --OCOR" or --NR".sub.2 group wherein R", equal to or different from R', has the same meaning as R'; PA1 m, n, p are numbers ranging: PA1 m from 0 to 3, n from 1 to 4 and p from 0 to 1; PA1 m+n+p is equal to 4. PA1 reaction of a Grignard or a MgR.sub.2 compound (R is hydrocarbyl) or of complexes MgR.sub.2 /Al-trialkyl with halogenating agents, as AlX.sub.3 or compounds AlR.sub.m X.sub.n (X is halogen, R is hydrocarbyl, m+n=3), SiCl.sub.4 or HSiCl.sub.3 ; PA1 reaction of a Grignard compound with a silanol or a polysiloxane, H.sub.2 O or with an alcohol and subsequent reaction with a halogenating agent or with TiCl.sub.4 ; PA1 reaction of Mg with an alcohol and with a hydrogen halide, or of Mg with a hydrocarbyl halide and with an alcohol; PA1 reaction of MgO with Cl.sub.2 or AlCl.sub.3 ; PA1 reaction of MgX.sub.2.nH.sub.2 O (X=halogen) with a halogenating agent or with TiCl.sub.4 ; PA1 reaction of Mg mono- or dialcoholates or of Mg carboxylates with a halogenating agent.
(1) an Al, Fe, Mn, Sb or Zn compound containing at least one metal-halogen bond; PA2 (2) a complex between an electron-donor compound and a Lewis acid chosen among the halides of the metals of Groups II-VIII of the Periodic System other than Ti; PA2 (3) a compound or composition inert towards the Mg halide and having a dielectric constant at 20.degree. C. higher than 2;
compounds (1), (2) and (3) being extractable from the solid for at least 30% by mols by treatment with toluene at 80.degree. C. for 2 hours, and the surface area of the solid after extraction being higher than 20 m.sup.2 /g.
Representative examples of the compounds indicated under (c)-(1) are: Al-dichloro-phenoxy, Al-monochloro-diphenoxy, Al-dichloro-xylenoxy, Al-monochloro-dixylenoxy, Al-dichloro-2,6-t-butyl-p-cresoxy, Al-dichloro-octoxy, Al-monoethyl-dichloride, Al-siloxyl-chloride, Zn-chloro-phenoxy, Zn-chloro-xylenoxy, Fe-dichloro-phenoxy, Mn-chloro-phenoxy.
The complexes indicated under (c)-(2) are selected particularly from: complexes of AlCl.sub.3 and SbCl.sub.3 with esters of aromatic monocarboxylic acids or with alkyl aryl ethers or diaryl ethers; complexes of SnCl.sub.4 with esters of aromatic monocarboxylic acids; complexes of ZnCl.sub.2 or FeCl.sub.3 with ethers or esters of monocarboxylic acids.
Representative compounds are the 1:1 complexes AlCl.sub.3 /ethyl benzoate, AlCl.sub.3 /anisole or phenetole, SnCl.sub.4 /ethyl benzoate, ZnCl.sub.2 /anisole, BF.sub.3 /diethyl ether.
The activators indicated under (c)-(3) include the compounds forming .pi.-bonds, such as, for instance, mesitylene, durene, hexamethylbenzene, anthracene, naphthalene, biphenyl, tetraphenylmethane, carbazole, phenanthrene, fluorene.
Other (c)-(3) compounds which can be employed are the halogenated hydrocarbons, such as, for instance, 1,2-dichloroethane, o-dichlorobenzene, hexachloroethane, n-butyl chloride, benzyl chloride, chloronaphthalenes, chloroform; the chlorosilanes, such as Si(C.sub.6 H.sub.5).sub.2 Cl.sub.2, SiCl.sub.3 CH.sub.3, Si(CH.sub.3).sub.3 Cl, Si(C.sub.2 H.sub.5).sub.3 Cl, (SiCH.sub.3 Cl.sub.2).sub.2 O; the polysiloxanes, such as polymethylsiloxane, hexamethyldisiloxane, octamethylcyclotetrasiloxane.
Other usable (c)-(3) compounds include anisole, chloroanisole, 2,4-dichloroanisole, bromophenetole.
As indicated, the activators are present in the catalyst component in an amount of at least 5% by mols with respect to the Mg halide.
Compounds (c)-(1) and (c)-(2) can be present at most in an amount equimolecular with respect to the Mg halide, while compounds (c)-(3) can be employed also in higher amounts consistently with the operative requirements of the preparation. Preferably, the activators are employed in molar ratios with respect to the Mg halide comprised between 0.1 and 0.3.
Preferably, in the preparation of the catalyst component (c), an electron-donor compound capable of forming complexes with MgCl.sub.2 and with Al-triethyl is also employed.
The preferred electron-donor compounds are selected from the alkyl and aryl esters of aromatic carboxylic acids, such as for example benzoic, toluic, p-methoxybenzoic and phthalic acid.
Representative esters are: ethyl benzoate, ethyl p-toluate, n-octyl phthalate, diisobutyl phthalate.
Other usable esters are the alkyl and aryl pivalates, maleates, malonates and acrylates.
The activators are added to the catalyst component during the preparation of the same; in some cases, such as for example that of the electron-donor/Lewis acid complexes and of some compounds containing metal-halogen bonds, they can be formed "in situ".
For example, by employing in the preparation of component (c) AlCl.sub.3 and ethyl benzoate and/or anisole, complexes of AlCl.sub.3 with said compounds are formed. Likewise, compounds containing Al-Cl bonds are formed by using Al-triphenoxy as a precursor of the compound (c)-(1) while operating in the presence of halogenating agents.
By Ti compounds supported on a Mg dihalide are meant the compounds not extractable from component (c) after treatment with toluene for 2 hours.
The treatment with toluene at 80.degree. C. for 2 hours is carried out on dispersions containing 5% by weight of solid. After said treatment at least 30% and preferably 40-70% by mols of the compounds employed as activators are extracted.
The surface area after extraction is higher than 20 m.sup.2 /g and preferably is comprised between 80 and 300 m.sup.2 /g.
Interesting results have been obtained with components (c) comprising, as activator, a .pi.-bonds forming compound containing one or more polyalkyl substituted aromatic rings, such as for instance durene and hexamethylbenzene, and an electron-donor compound complying with the criterion of being extractable from component (c) for at least 70% by mols by treatment with Al-triethyl in the standard conditions specified hereinafter.
Representative classes of these compounds are the esters of ortho-dicarboxylic acids, the esters of monocarboxlylic acids containing at least one branched group linked to the carboxyl group, the esters of carbonic acid, the esters of unsaturated dicarboxylic acids.
The standard conditions of the reaction with AlEt.sub.3 are: into a flask of 5 liters holding capacity are introduced 4 liters of anhydrous and deaerated n-heptane containing 20 mMoles Al(C.sub.2 H.sub.5).sub.3. The temperature is raised to 70.degree. C., about 1 g of solid catalyst component is introduced and the whole is allowed to react under stirring for 15 minutes. It is cooled rapidly to 0.degree. C. and filtered, thus isolating a solid which is dried under vacuum at 25.degree. C. and analyzed.
In the catalyst components (c) comprising an electron-donor compound, the latter is employed in an amount corresponding to a molar ratio with respect to the Mg dihalide comprised between 0.05 and 0.5.
Preferably, the activator is selected from the Al compounds containing at least one Al-halogen bond, the complexes of AlCl.sub.3 or SbCl.sub.3 with esters of aromatic monocarboxylic acids, as for example ethyl benzoate, or with ethers, as for example diisoamyl ether, anisole, phenetole, and the compounds forming .pi.-bonds, such as hexamethylbenzene and durene.
As indicated, the complexes and the compounds containing metal-halogen bonds can be formed "in situ". Valuable results have been obtained by employing mixtures of the compounds (c)-(1) and (c)-(2), preformed or formed "in situ", and optionally (c)-(3), to which an electron-donor compound has also been added. The activator (c)-(3) is preferably employed in admixture with an electron-donor compound.
Components (a), (b) and (c) are caused to react with each other in any order; nevertheless, preferably components (a) and (b) are premixed before being contacted with component (c).
Component (c) can be premixed with component (a) and/or with component (b). Premixing of (a) and (b) is performed at temperatures usually comprised between room temperature and the polymerization temperature.
The pre-reaction of (c) and (b) can be carried out also at higher temperatures. Compound (b) can also be incorporated in and made to react with component (c) itself.
Component (b) is reacted in a molar ratio with respect to the halogenated Ti compound supported on component (c) of at least 1, and in a molar ratio with respect to the Al-alkyl compound employed as component (a) lower than 20 and preferably comprised between 0.05 and 1. Ratios higher than 1 can be employed in the case of compounds (b) not complexing or complexing only weakly with Al-triethyl also in conditions promoting the formation of the complex.
In component (c), the molar ratio between the Mg dihalide and the halogenated Ti compound supported on it is comprised between 1 and 500, and the molar ratio between the halogenated Ti compound and the electron-donor, both supported on the Mg dihalide, is comprised between 0.1 and 50.
The electron-donor compound as defined in (b) does not show at the equivalent point of the titration test with Al-triethyl (carried out under the standard conditions indicated hereinafter) any logarithmic variation of potential, i.e., a wave, in the titration curve.
A completely different situation occurs in the case of amines like isoquinoline or esters like ethyl-p-toluate or ethylbenzoate, wherein the titration curve shows a wave at the equivalent point. The absence of a wave at the equivalent point indicates that electron-donor compound (b) is present, at least in part, in non-complexed form with Al-triethyl.
Electron-donor compounds containing active hydrogen atoms reactive towards Al-triethyl, i.e., capable of substitution reactions with Al-triethyl, are prereacted with Al-triethyl, before subjecting the same to the complexation test. In the titration test the equivalent point is generally referred to the use of 1 mol of Al-triethyl per mol of donor.
Compounds (b) can be used in mixture, in a wide range, with donors forming complexes with Al-triethyl when titrated according to the test set forth above.
The titration of the mixtures containing significant amounts of the complexing donors, shows the potential variation due to the presence of said complexing donors.
However, the polymerization performance of the catalysts obtained by using the above mixtures as component (b) is not significantly reduced by the presence of the complexing donor.
The compound (b) is chosen in particular from the compounds of general formula EQU R.sub.m SiY.sub.n X.sub.p
wherein:
Preferred silicon compounds are: phenyl alkoxy silanes, such as phenyl triethoxy or phenyl trimethoxy silane, diphenyl dimethoxy and diphenyl diethoxy silane, monochloro-phenyl diethoxy silane.
In the catalysts of the invention the silicon compound is present, in combined form in the solid product of the reaction between the various components which form the catalyst, in a molar ratio silicon compound/halogenated Ti compound higher than 0.05 and in general comprised between 0.1 and 5.
Other suitable compounds (b) are: 2,2,6,6-tetramethyl-piperidine, 2,2,5,5-tetramethylpyrrolidine, 2,2,6,6-tetramethyl-piperidide-Al-diethyl, di(m-methylphenyl)amine, succinimide, 2,2,6,6-tetramethyl-tetrahydro-4-pyrone, Al-dichloro-monophenoxy.
Examples of Al-alkyl compounds constituting the component (a) are the Al-trialkyls, such as for instance AlEt.sub.3, AlEt.sub.2 H, Al-triisobutyl, Al-triisopropyl, and compounds containing two or more Al atoms linked to each other through hetero-atoms, as ##STR1##
As indicated, Al-alkyl compounds in which Al atoms are linked to each other through SO.sub.4 or SO.sub.3 groups are also suitable.
The Al-alkyl compounds can be employed in admixture with alkyl-Al halides, as AlEt.sub.2 Cl. Component (c) is prepared according to several methods. One of these consists in co-grinding the Mg halide, the activator, the Ti compound and, optionally, the electron-donor compound until the product, after extraction with toluene at 80.degree. C. for 2 hours, shows a surface area higher than 20 m.sup.2 /g. In this co-grinding the order of addition of the various compounds is not important.
Preparations of this type are described in U.S. Pat. No. 4,107,413.
According to another method, the anhydrous Mg halide in active form, as hereinafter defined, is hot-treated (40.degree.-80.degree. C.) with a solution of the activator in an aromatic or halogenated hydrocarbon solvent and subsequently with a hydrocarbon solution of the Ti compound. The resulting suspension is employed as catalyst component.
When operating according to this method, it is preverable to use an activator chosen among the complexes Lewis acid/Lewis base.
Another method consists in co-grinding the Mg halide and the activator or a precursor of the latter, for instance a Lewis acid such as AlCl.sub.3, per se not extractable with toluene under the specified standard conditions, until activation of the Mg halide, in treating the ground product with a solution, in an aromatic or halogenated hydrocarbon, of an electron-donor compound capable of forming complexes with the Lewis acid, and in adding the Ti compound dissolved in a hydrocarbon.
The resulting suspension is employed as catalyst component.
In general, the concentration of the solids in the suspensions is comprised between 10 and 50% by weight based on the solvent.
Suitably, the catalyst component is pre-treated, before the reaction with the Al-alkyl compound, with an aromatic or halogenated hydrocarbon solvent, such as toluene or 1,2-dichloroethane, at a temperature comprised between room temperature and the boiling point of the solvent for a time sufficient for at least partially solubilizing the activator.
The suspension, in which the solids concentration is in general comprised between 1 and 50% by weight, is then employed as such as catalyst component.
In all the above methods, the final product contains a Mg dihalide present in the active form as defined hereinafter. For "active form of the Mg dihalide" is meant the Mg dihalides showing in the X-rays powder spectrum of component (c) a broadening of at least 30% of the most intense diffraction line which appears in the powder spectrum of the corresponding dihalide having a surface area of 1 m.sup.2 /g, or is meant the Mg dihalides showing an X-rays spectrum in which said most intense diffraction line is replaced by a halo with its intensity peak shifted with respect to the interplanar distance of the most intense line.
Very active forms of Mg dihalides are those showing an X-ray powder spectrum in which the most intense diffraction line appearing in the spectrum of the corresponding halide having a surface area of 1 m.sup.2 /g has a decreased intensity and is broadened to form a halo, or are those in which said most intense line is replaced by a halo having its intensity peak shifted with respect to the interplanar distance of the most intense line. In general, the surface area of the above mentioned forms is higher than 20-40 m.sup.2 /g and in particular is comprised between 100 and 300 m.sup.2 /g. The surface area is determined on component (c) after extraction with toluene at 80.degree. C. for 2 hours. The value thus obtained is considered as the surface area of the Mg halide.
Preferred Mg dihalides are MgCl.sub.2 and MgBr.sub.2. The water content of the dihalides in general is lower than 1% by weight.
Other known methods for the preparation of a Mg dihalide in active form or of catalyst components containing Ti and supported on a Mg dihalide, in which the dihalide is present in the active form, are based on the following reactions:
The Ti compounds containing at least one Ti-halogen bond include in particular the Ti tetrahalides, the Ti trihalides and dihalides and the Ti trihalogen-alcoholates.
Preferred compounds are: TiCl.sub.4, TiBr.sub.4, 2-6,dimethyl-phenoxy-trichloro-titanium and trichloro-phenoxy-titanium. In the case of the Ti halogen-alcoholates, these compounds can be formed "in situ" by suitable exchange reactions between the various compounds employed in the preparation of the catalyst component. In the preferred catalysts, the component (c) is obtained from MgCl.sub.2, TiCl.sub.4 or Cl.sub.3 TiOC.sub.6 H.sub.5 and complexes, even formed "in situ", between AlCl.sub.3 and ethyl benzoate and/or ethers, such as anisole or phenetole, and component (b) is phenyl or ethyl triethoxy silane or diphenyl dimethoxy silane or diphenyl diethoxy silane.
Component (a) is an Al-trialkyl, as Al-triethyl or Al-triisobutyl.
The catalysts according to the invention are employed for polymerizing the alpha-olefins according to known procedures, that is by carrying out the polymerization in liquid phase, either in the presence or in the absence of an inert hydrocarbon solvent, or in gaseous phase or also by combining, for instance, a polymerization step in liquid phase with a step in gaseous phase.
In general, the temperature is comprised between 40.degree. and 160.degree. C., but preferably between 60.degree. and 90.degree. C., while operating either at atmospheric pressure or at a higher pressure.
As a molecular weight regulator hydrogen or another regulator of known type can be employed.
The catalysts are particularly suitable for the polymerization of propylene, butene-1, styrene and 4-methyl-pentene-1. The catalysts can also be employed for polymerizing according to known methods, mixtures of propylene and ethylene to produce modified polypropylenes having improved impact resistance at low temperatures (the so called block copolymers of propylene and ethylene) or to obtain crystalline random copolymers of propylene with minor amounts of ethylene.
The test for determining the capability of compound (b) of forming complexes is performed by using a potentiograph Metrohm model E 536 equipped with titration bench E 535, automatic burette E 552, magnetic stirrer E 549 and titration cell EA 880. A combined electrode EA 281 (Pt//Ag/AgCl/KCl 3M) is employed.
As a titrating agent there is employed a 0.5M hexane solution of Al-triethyl, which is added to a 0.5M benzene solution of the compound under analysis. It is operated at room temperature in a nitrogen atmosphere. The test of reactivity of the electron-donor compound with MgCl.sub.2 is performed under the following conditions:
Into a 500 cc flask are introduced, in a nitrogen atmosphere, 2 g MgCl.sub.2 (21 mMoles) suspended in 200 cc toluene and 3.5 mMoles of the electron-donor under analysis. It is allowed to react at 25.degree. C. for 1 hour and the solid is filtered and washed with 200 cc toluene and subsequently with 200 cc n-heptane. The solid is isolated, dried and analyzed.
As MgCl.sub.2 is employed the product obtained from MgCl.sub.2.2.5C.sub.2 H.sub.5 OH by reaction with Al-triethyl according to the following procedure: into a 3000 cc flask are introduced 2340 cc of a 0.83M hexane solution of Al(C.sub.2 H.sub.5).sub.3 ; while keeping the temperature below 10.degree. C., little by little are added 136 g MgCl.sub.2.2.5C.sub.2 H.sub.5 OH. After completion of the addition, the mixture is heated at 70.degree. C. for 4 hours; thereupon it is filtered and the solid is washed repeatedly with n-heptane and is dried under vacuum (0.2-0.5 Torr).
The surface area of the MgCl.sub.2 thus obtained amounts to 618 m.sup.2 /g and the pores volume to 0.532 cc/g.
The following non-limiting examples are given to illustrate the invention in even more detail.